feat(issues): Include empty tags in group tags endpoint (#102049)

Add support for including empty tag values in the group tags endpoint
(api/0/issues/{id}/tags/) when the
organizations:issue-tags-include-empty-values feature flag is enabled.

Makes a 2nd snuba query and attaches the empty values. I couldn't figure
out how to make this work in a single snuba query, but i did figure out
how to do this without N snuba queries.

also needs some follow up frontend work

<img width="454" height="256" alt="image"
src="https://github.com/user-attachments/assets/6b935125-7ed5-4418-bcbb-f4bbc7349990"
/>

part of https://linear.app/getsentry/issue/RTC-1181/

Author: scttcper

src/sentry/features/temporary.py

@@ -193,6 +193,8 @@ def register_temporary_features(manager: FeatureManager) -> None:
     manager.add("organizations:issue-detection-sort-spans", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Whether to allow issue only search on the issue list
     manager.add("organizations:issue-search-allow-postgres-only-search", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=False)
+    # Include empty tag count in issue tag totals/values
+    manager.add("organizations:issue-tags-include-empty-values", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=False)
     # Enable the new issue category mapping
     manager.add("organizations:issue-taxonomy", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     manager.add("organizations:metric-issue-poc", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)

src/sentry/issues/endpoints/group_tags.py

@@ -5,7 +5,7 @@
 from rest_framework.request import Request
 from rest_framework.response import Response
 
-from sentry import tagstore
+from sentry import features, tagstore
 from sentry.api.api_publish_status import ApiPublishStatus
 from sentry.api.base import region_silo_endpoint
 from sentry.api.helpers.environments import get_environments
@@ -62,12 +62,19 @@ def get(self, request: Request, group: Group) -> Response:
 
         environment_ids = [e.id for e in get_environments(request, group.project.organization)]
 
+        include_empty_values = features.has(
+            "organizations:issue-tags-include-empty-values",
+            group.project.organization,
+            actor=request.user,
+        )
+
         tag_keys = backend.get_group_tag_keys_and_top_values(
             group,
             environment_ids,
             keys=keys,
             value_limit=value_limit,
             tenant_ids={"organization_id": group.project.organization_id},
+            include_empty_values=include_empty_values,
         )
 
         data = serialize(tag_keys, request.user)

src/sentry/tagstore/base.py

@@ -301,6 +301,7 @@ def get_group_tag_keys_and_top_values(
         keys: list[str] | None = None,
         value_limit=TOP_VALUES_DEFAULT_LIMIT,
         tenant_ids=None,
+        include_empty_values=False,
         **kwargs,
     ):
 

src/sentry/tagstore/snuba/backend.py

@@ -684,6 +684,7 @@ def get_group_tag_keys_and_top_values(
         keys: list[str] | None = None,
         value_limit: int = TOP_VALUES_DEFAULT_LIMIT,
         tenant_ids=None,
+        include_empty_values=False,
         **kwargs,
     ):
         # Similar to __get_tag_key_and_top_values except we get the top values
@@ -726,7 +727,28 @@ def get_group_tag_keys_and_top_values(
             tenant_ids=tenant_ids,
         )
 
-        # Then supplement the key objects with the top values for each.
+        if include_empty_values:
+            keys_to_check = list(values_by_key.keys()) or [k.key for k in keys_with_counts]
+            empty_stats_map = self.__get_empty_value_stats_map(
+                dataset=dataset,
+                filters=filters,
+                conditions=conditions,
+                keys_to_check=keys_to_check,
+                tenant_ids=tenant_ids,
+                start=kwargs.get("start"),
+                end=kwargs.get("end"),
+            )
+            for k, stats in empty_stats_map.items():
+                if not stats or stats.get("count", 0) <= 0:
+                    continue
+                vals = values_by_key.get(k, {})
+                vals[""] = stats
+                # Re-sort after adding empty count and trim to value_limit
+                sorted_items = sorted(vals.items(), key=lambda kv: (-kv[1]["count"], str(kv[0])))[
+                    :value_limit
+                ]
+                values_by_key[k] = {vk: vd for vk, vd in sorted_items}
+
         for keyobj in keys_with_counts:
             key = keyobj.key
             values = values_by_key.get(key, dict())
@@ -744,6 +766,61 @@ def get_group_tag_keys_and_top_values(
 
         return keys_with_counts
 
+    def __get_empty_value_stats_map(
+        self,
+        dataset: Dataset,
+        filters: dict[str, list[Any]],
+        conditions: list,
+        keys_to_check: list[str],
+        tenant_ids: dict[str, int | str] | None,
+        start,
+        end,
+    ) -> dict[str, dict[str, Any]]:
+        if not keys_to_check:
+            return {}
+
+        empty_alias_map: dict[str, dict[str, str]] = {}
+        selected_columns_empty: list[list] = []
+        for i, k in enumerate(keys_to_check):
+            cnt_alias = f"empty_cnt_{i}"
+            min_alias = f"empty_min_{i}"
+            max_alias = f"empty_max_{i}"
+            empty_alias_map[k] = {"count": cnt_alias, "first": min_alias, "last": max_alias}
+            tag_expr = self.format_string.format(k)
+            empty_predicate = ["equals", [tag_expr, ""]]
+            selected_columns_empty.append(["countIf", [empty_predicate], cnt_alias])
+            selected_columns_empty.append(["minIf", [SEEN_COLUMN, empty_predicate], min_alias])
+            selected_columns_empty.append(["maxIf", [SEEN_COLUMN, empty_predicate], max_alias])
+
+        empty_filters = dict(filters)
+        if self.key_column in empty_filters:
+            # For empty-value stats, do not restrict by tags_key; events that
+            # store an empty value may omit the key entirely. Removing this
+            # filter ensures those events are counted.
+            del empty_filters[self.key_column]
+
+        empty_results = snuba.query(
+            dataset=dataset,
+            start=start,
+            end=end,
+            groupby=None,
+            conditions=conditions,
+            filter_keys=empty_filters,
+            aggregations=[],
+            selected_columns=selected_columns_empty,
+            referrer="tagstore._get_tag_keys_and_top_values_empty_counts",
+            tenant_ids=tenant_ids,
+        )
+        stats_map: dict[str, dict[str, Any]] = {}
+        for k in keys_to_check:
+            aliases = empty_alias_map[k]
+            stats_map[k] = {
+                "count": empty_results.get(aliases["count"], 0),
+                "first_seen": empty_results.get(aliases["first"]),
+                "last_seen": empty_results.get(aliases["last"]),
+            }
+        return stats_map
+
     def get_release_tags(self, organization_id, project_ids, environment_id, versions):
         filters = {"project_id": project_ids}
         if environment_id:

tests/sentry/issues/endpoints/test_group_tags.py

@@ -304,6 +304,81 @@ def test_device_class(self) -> None:
         assert top_values[1]["value"] == "low"
         assert top_values[2]["value"] == "medium"
 
+    def test_include_empty_values_for_specific_key_with_feature(self) -> None:
+        event = self.store_event(
+            data={
+                "fingerprint": ["group-empty-all"],
+                "tags": {},
+                "timestamp": before_now(minutes=1).isoformat(),
+            },
+            project_id=self.project.id,
+            assert_no_errors=False,
+        )
+        self.store_event(
+            data={
+                "fingerprint": ["group-empty-all"],
+                "tags": {"foo": "bar"},
+                "timestamp": before_now(minutes=1).isoformat(),
+            },
+            project_id=self.project.id,
+        )
+
+        self.login_as(user=self.user)
+
+        url = f"/api/0/issues/{event.group.id}/tags/?key=foo"
+
+        # Off by default: empty should be excluded from topValues
+        response = self.client.get(url, format="json")
+        assert response.status_code == 200
+        assert len(response.data) == 1
+        values = {v["value"] for v in response.data[0]["topValues"]}
+        assert values == {"bar"}
+
+        # With feature: empty should be included
+        with self.feature({"organizations:issue-tags-include-empty-values": True}):
+            response = self.client.get(url, format="json")
+        assert response.status_code == 200
+        values = {v["value"] for v in response.data[0]["topValues"]}
+        assert values == {"", "bar"}
+        assert response.data[0]["topValues"][0]["count"] == 1
+
+    def test_include_empty_values_in_all_tags_with_feature(self) -> None:
+        event = self.store_event(
+            data={
+                "fingerprint": ["group-empty-all-tags"],
+                "tags": {"foo": ""},
+                "timestamp": before_now(minutes=1).isoformat(),
+            },
+            project_id=self.project.id,
+            assert_no_errors=False,
+        )
+        self.store_event(
+            data={
+                "fingerprint": ["group-empty-all-tags"],
+                "tags": {"foo": "bar"},
+                "timestamp": before_now(minutes=1).isoformat(),
+            },
+            project_id=self.project.id,
+        )
+
+        self.login_as(user=self.user)
+        url = f"/api/0/issues/{event.group.id}/tags/?limit=10"
+
+        # Off by default: empty should be excluded from the All Tags list
+        response = self.client.get(url, format="json")
+        assert response.status_code == 200
+        foo = next((t for t in response.data if t["key"] == "foo"), None)
+        assert foo is not None
+        assert {v["value"] for v in foo["topValues"]} == {"bar"}
+
+        # With feature: empty should be included in the All Tags list
+        with self.feature({"organizations:issue-tags-include-empty-values": True}):
+            response = self.client.get(url, format="json")
+        assert response.status_code == 200
+        foo = next((t for t in response.data if t["key"] == "foo"), None)
+        assert foo is not None
+        assert {v["value"] for v in foo["topValues"]} == {"", "bar"}
+
     def test_flags(self) -> None:
         event1 = self.store_event(
             data={